Adenosine is an important inhibitory neuromodulator. It inhibits firing of cholinergic cells of the lateral dorsal tegmental nucleus (LDT), and this action is thought to be related to the effects of adenosine on arousal. Little is known about the molecular regulation of adenosine levels in the extracellular space. Work by the applicant and others using various preparations has provided evidence that monamines, peptides, and metabotropic glutamate agonists regulate adenosine levels by a mechanism dependent upon cyclic AMP metabolism. In addition, in cortical cultures, the hippocampal slice preparation, and lDT, the cyclic nucleotide phosphodiesterase inhibitor zaprinast evokes significant extracellular adenosine accumulation. Since the LDT receives glutamatergic, monoaminergic, and peptidergic inputs, mechanisms linking adenosine accumulation with neurotransmitter control of cyclic nucleotide metabolism may be important in regulating extracellular adenosine levels in the LDT. The specific hypothesis to be tested in this proposal is that cyclic nucleotides play a critical role in the regulation of adenosine levels in the LDT. The specific aims of this project are to: (1) Use Molecular cloning techniques to characterize the phosphodiesterases present in the LDT; (2) Characterize the effect of phosphodiesterase inhibitors on adenosine accumulation and cyclic nucleotide metabolism in the LDT; (3) Characterize the effect of endogenous modulators on adenosine accumulation and cyclic nucleotide metabolism in the LDT. It is hoped that this work will further our understanding of how adenosine levels are regulated at a molecular level, how sleep related changes in adenosine levels might be produced, and whether such changes play a causal role in the determination of behavioral state.